The invention is directed to sensors for electrochemical analysis, in particular for measurements which are carried out within a living body.
Ion selective, gas sensitive and enzymic sensing electrodes have in recent times attained considerable importance and recognition for several types of electrochemical measurements, in particular in the physiology and pathophysiology. It has been found desirable in many cases that such measurements take place in a precisely predeterminable location in the living body. In order to succeed in solving this problem the sensing electrodes must be constructed in the form of a catheter.
In many cases it is desirable to measure several different parameters, for example different types of ions, different types of gases or combinations thereof. The introduction of numerous catheters at the same time is however hardly possible in most cases. Even if it were possible to insert several catheters at short time intervals in the patient such a procedure would cause considerable strain and discomfort to the patient.
Multi-measuring probes have been developed which make it possible to carry out simultaneous measurement of several parameters. Unfortunately the introduction of such multi-probes having multielectrodes into a catheter of rather small diameter creates considerable practical difficulties. In addition to this such catheters with multielectrodes are extremely expensive; in particular in intensive care situations several groups of patients must be provided with such catheter-electrodes and these catheter-electrodes must be watched and serviced simultaneously.
In the continuous measurement of dissolved oxygen in fermentation cultures it has been suggested that the well-known platinum electrode (in accordance with Clark) be divided into two structural parts, namely a portion having a cathode and an anode on one hand and on the other hand an outer body for supporting the membrane necessary for the stabilization of the oxygen diffusion (K. Ring, S. Schlecht, W. Eschweiler and J. Kutscher: An Electrode for the Continuous Measurement of Dissolved Oxygen (pO.sub.2) in Fermentation Cultures (title translation), Archiv fur Mikrobiologie, vol. 65, 1969, p.48-60).
In this procedure there is provided a sheath which serves as the outer body, which can be sterilized with the fermentation vessel. The measuring probe comprising the cathode and the anode is introduced into the sheath. The connection between the cathode and the anode is obtained by introducing an electrolyte into the outer body, that is to say the sheath. The membrane operates as a stabilizer in the continuous measurement process and further separates the measuring portion of the measuring arrangement from the culture itself, so that a contamination of the measuring probe is avoided. Without the membrane it would not be possible to obtain a stable reading and also not be possible to plot the polarographic measuring curve. In order to obtain proper spacing the platinum electrode of the probe is covered with a further membrane which, in the operating position, is in direct contact with the outer membrane. Thus the diffusion path of the oxygen is stabilized and held constant, so that the measurement thereof is less influenced by turbulence in the test solution. The combination of measuring probe and sheath therefore provides a selfcontained complete item which may be utilized for the measurement of the partial pressure of oxygen but is not suitable for any other purpose.